Linear adjusting motions are needed in many industrial areas. Linear drive devices, which transform a rotary drive motion, for example, of an electric motor, into a translatory motion by means of a spindle and a nut arranged on the spindle, are often used to generate this motion. The nut is secured here against rotary motions, as a result of which it performs a purely translatory motion. This motion of the nut is utilized as an adjusting motion for a load to be moved. Possible applications of such linear drive devices are, for example, lifting columns, linear drives and the like.
It was found that various circumstances may lead to failure of the nut, especially of the thread of the nut. Without taking safety measures against this, the nut would be freely mobile on the spindle. This may lead to considerable damage to the load and the linear drive device especially in case of vertical orientation of the spindle and heavy loads. If persons or loads located in the vicinity of persons are to be moved with such drives, these persons are at great risk.
Systems with safety nuts, which begin to act when the nut that has the carrying function during normal operation fails, have therefore already been developed. The safety nut usually has a thread for this, which does not bear the load as long as the main nut does and consequently has not yet failed. The safety nut is prevented for this purpose from performing a rotary motion, so that the safety nut cannot run up on the flank of the main nut and the thread of the safety nut cannot mesh with the thread of the spindle as a result.
It was therefore already proposed in EP 1 134 454 A1 that a metallic safety nut be arranged at one end of the main nut in a hollow cylindrical recess, which is provided with two diametrically opposed carriers. On its circumferential surface, the safety nut is provided with four notches offset by 90° each in relation to one another. With two of its notches, the safety nut meshes with these two carriers and is thus aligned in relation to the main nut in reference to its rotary position. However, it is to be feared that despite this arrangement during the mounting of the safety nut and the main nut on the spindle, a considerable adjustment effort is needed for the exact alignment of the three elements. If exact alignment of these three elements is not carried out, this may lead to failure of the safety nut. In addition, this arrangement permits the linear drive device to operate either only as a pulling drive or only as a pushing drive depending on the order in which the main nut and the safety nut are arranged in relation to the direction of load of the drive.